Tensions between Russia and Ukraine have left Moscow on the outs with Germany, France, Britain and the U.S. Those countries are partnered with Russia in talks with Iran over its nuclear program.

DAVID GREENE, HOST:

Now there is disagreement over who is causing that instability in Eastern Ukraine. Moscow says it is people who long to be part of Russia just expressing themselves freely.

The West has accused Russia of instigating. And there are fears this could spill over into other areas of diplomacy - like the long-running talks with Iran over its nuclear program. Russia has played a key role there, but now they're becoming the odd man out with many of the other countries involved - the United States, Germany, France and Britain.

The Iran talks continue this week in Vienna, and Iran says they are approaching the most difficult phase - the drafting of an actual written agreement.

NPR's Peter Kenyon has been covering these talks and he joins us from Istanbul. Peter, good morning.

PETER KENYON, BYLINE: Morning, David.

GREENE: So we have talked about the fear that diplomats have had, that this Ukraine crisis could impact these talks on Iran. So far they've been going forward. Is there still reason to be concerned here?

KENYON: I'd say there is. After the last round in March, Russia warned that if these sanctions and pressures over Ukraine continue against Russia, it might be forced to change its approach in these Iran talks. Since then, there's been accounts of a deal that might allow Iran to sell more oil than it's currently allowed to. So, that's got people nervous. But analysts say if Moscow is really waiting to disrupt these talks, it might happen later in the process when there's more at stake. Of course, the U.S. and its allies don't want Iran to have a nuclear weapon and Iran wants these punitive sanctions lifted that are strangling its economy. So, it could be that these negotiators are slowly moving towards a very high-pressure situation in which all kinds of issues could intrude.

GREENE: Well, let's talk about potentially another source of tension that might disrupt these talks. It's between Washington and Tehran over Iran's pick to be its next ambassador to the United Nations. Explain that for us.

KENYON: Well, Iran chose a man named Hamid Aboutalebi. He's an experienced diplomat. He's been posted to Italy, the EU, Australia, elsewhere. But in Washington, alarm bells went off because there he's known for having a role in the 1979 hostage crisis at the U.S. embassy in Tehran. Aboutalebi says he wasn't there when it was taken over. He only came in later to do a little translating. But the Senate has already voted not to allow him entry into the U.S. The White House now says the Iranian nominee is not viable. Tehran says it's waiting for a formal response but it's really none of the U.S.'s business who they pick for the U.N. So, it's another issue to be watched, if only because this seems to be the first time since taking office that Iranian President Hasan Rouhani may have made a political misstep. He probably should have known that this would raise red flags in Washington.

GREENE: But, Peter, for people who want these talks to succeed, I mean, if you take a cup-half-full approach at least, the fact is they are still going forward. I mean, people are still talking in Vienna. And the Iranians are saying this is coming to an important moment where something has to be written, some kind of agreement. I mean, take us into the process. Where are we?

KENYON: Well, I would say the Iranians have been cautiously upbeat, which is encouraging if you want these to succeed. There's always these expert-level talks before these meetings begin where a lot of the thorny details get hashed out. And after this latest expert-level round, Iran said things were going quite well. And then last night, one of the top negotiators, Deputy Foreign Minister Abbas Araghchi, confirmed that the talks are going well enough that they are considering the actual drafting at the next round. Here's how he put it.

ABBAS ARAGHCHI: I think we have been, to some extent, successful so far. Discussions have been somehow productive and we think that we are almost ready to go into drafting next time we meet in May.

KENYON: Now, we have to add that the drafting is the most difficult part. It's no guarantee of success, but the fact that they're willing to start suggests that they might be trying to finish this up this summer rather than extending it to next winter, which is one option.

GREENE: And Peter, much of what happens at these talks happen quietly and behind closed doors. And Washington has actually been quietly having one-on-one meetings with the Iranian government. I mean, is that becoming an important part of the communications here?

KENYON: I think this could become a big deal at some point. There was a 90-minute meeting last night. The U.S. description of it was useful and professional and it was not limited to just nuclear issues. The U.S. raised the case of three Americans currently held in Iran. So, this is gradually becoming a forum for Washington and Tehran, two countries that haven't spoken much, to exchange information. Many analysts say that's long overdue.

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